The present invention is directed to a high-speed charge-mode controller for use with a switched-mode power converter.
Power converters are used in modem electronic equipment to convert relatively poorly regulated direct current (DC) power supply voltages to highly regulated DC power supply voltages. Such devices are used, for example, to power microprocessors and similar devices. Current technology microprocessors can require 1.5 volts or less of supply voltage at peak levels exceeding 80 amperes (A). Because such devices are often switched at rates exceeding 1.5 GHz, they routinely experience current slew rates of 400 A/microsecond (xcexcSec) or more. As a result, it has become necessary in recent years to provide such devices with power from a multi-phase voltage regulator. The multi-phase voltage regulator typically obtains its power from a single relatively poorly regulated power supply and provides a number of sources (phases) of highly regulated voltage for use by the device.
In the past, peak input current mode (PICM) control has been used to control some multi-phase controllers, such as the Semtech SC-2422, SC-2425, SC-2424, SC-2433 and SC-2434 models available from Semtech Corporation of Newbury Park, California. In such PICM systems, current sensing is realized on the input positive rail of the power converter by using a low value (e.g., 0.002-0.005 Ohm) current sensing resistor. The PICM-type approach generally works well and has the advantages that: (1) phase currents are automatically balanced; (2) active voltage positioning is easily implemented with very good precision; (3) the wide control bandwidth settles the output to its correct position very quickly; and (4) module current sharing can be implemented.
Although PICM has these merits, it also has some shortcomings. These are: (1) the leading edge spike of the MOSFET (metal oxide semiconductor field effect transistor) current needs to be filtered out; (2) parasitics in the layout tend to interact with the sensing filter to cause ringing and limit operational frequencies to about 500 KHz per phase at 5 volts input and 250 KHz per phase at 12 volts input; (3) in order to avoid overlapping of the current pulses coming from different phases (a requirement of this approach) multiple sensing resistors and current amplifiers are required. This last shortcoming adds to system cost and IC (integrated circuit) pin count. The maximum duty cycle of the PWM (pulse with modulation) pulses is also limited depending on the configuration to less than 50% for a two-phase controller, less than 33% for a three-phase controller, etc. This limits the applications in which such a controller may be used.
Accordingly, it would be desirable to provide a high-speed controller which could operate on multiple phases with no duty cycle overlap limitation and no requirement for multiple current sensing devices.
A multiphase controller for a PWM power converter employs a single current sense device to measure input current, I, and an integrator at each phase to accurately measure power delivered during a pulse. The integrator monitors current delivered through a circuit which delivers a current signal scaled to I/N where N is the number of active phases. Thus where there are three overlapping phases, one-third of I is delivered to the integrator for each phase that is on or active. The integrator provides a Charge Ramp signal to an input of a Pulse Width Modulation (PWM) comparator associated with each phase. The other input of the PWM comparator is tied to an error control signal common to all of the phases. When the Charge Ramp signal and the error control signal match, the corresponding phase is turned off for the duration of the cycle.